1. Field of the Invention
The present invention relates to a color compensation multi-layered member for a display apparatus, an optical filter for a display apparatus having the same, and a display apparatus having the same, and more particularly, to a color compensation multi-layered member for a display apparatus that may reduce a difference in a color change depending on an increase in a viewing angle to thereby improve the viewing angle performances, an optical filter for a display apparatus having the same, and a display apparatus having the same.
2. Description of Related Art
As modern society becomes more information oriented, technology of parts and devices related to information displays is remarkably advancing, and these parts and devices are becoming widespread. Display apparatuses utilizing parts and devices related to photoelectronics are becoming significantly widespread and used for television apparatuses, monitor apparatuses of personal computers, and the like. Also, display apparatuses are becoming both larger and thinner.
In general, Liquid Crystal Display (LCD) apparatuses are one of flat panel display apparatuses displaying images using liquid crystal. The LCD apparatuses are relatively thinner and lighter, and have relatively lower driving voltage and consumption power in comparison with other display apparatuses to thereby being widely used.
FIG. 1 is a schematic diagram illustrating a basic structure and driving principle of a Liquid Crystal Display (LCD). As illustrated in FIG. 1, two polarizing films 110 and 120 are attached on a conventional vertical alignment (VA) mode LCD in such a manner as to be perpendicular to each optical axis. Liquid crystal molecules 150 having birefringence characteristics are inserted and arranged between two transparent substrates 130 coated with a transparent electrode 140, and thereby the liquid crystal molecules 150 are moved perpendicularly to an electric field and arranged when the electric field is applied by a driving power unit 180. In this instance, a light from a backlight unit becomes a linearly polarized light after passing through a first polarizing film 120. As illustrated in a left side of FIG. 1, the liquid crystal is aligned perpendicularly to the substrate when OFF, so that the linearly polarized light may be maintained as is, thereby failing to pass through a second polarizing film 110 perpendicular to the first polarizing film 120. As illustrated in a right side of FIG. 1, the liquid crystal is horizontally aligned between the optical axes of the two polarizing films 110 and 120 perpendicular to each other in a direction parallel to the substrate due to the electric field when ON, so that a polarization state of the linearly polarized light obtained through the first polarizing film is changed into a circular polarization state or an elliptically polarization state immediately before the linearly polarized light reaches the second polarizing film while passing through the liquid crystal molecules, thereby passing through the second polarizing film. When the applied electric field is adjusted, alignment states of the liquid crystal may be gradually changed from vertical alignment to horizontal alignment, and thereby the light intensity is adjusted.
FIG. 2 is a schematic diagram illustrating an alignment state and optical transmission of liquid crystal displays depending on viewing angles.
Alignment states of the liquid crystal molecules may be differently visible depending on viewing angles when liquid crystal molecules within a pixel 220 are aligned in a certain direction. The alignment state of the liquid crystal molecules is visible to be nearly horizontal alignment 212 as viewed from a right direction 210 with respect to the normal direction 230 of the LCD screen, and thus the screen is visible to be relatively brighter. The alignment state of the same is visible to be nearly identical to that of the liquid crystal molecules within the pixel 220 as viewed from a normal direction 230 of the screen. The alignment of the same is visible to be vertical alignment 252 as viewed from a left direction 250 with respect to the normal direction of the screen, and thus the screen is visible to be relatively darker.
Thus, the LCD may exhibit changes in light intensity and color depending on the change in the viewing angle, and have large limitations in the viewing angle performances comparing with self-light emitting display apparatuses. Accordingly, many studies have been made to improve the viewing angle performances.
FIG. 3 is a schematic diagram illustrating an example of a conventional invention for improving change in a contrast ratio and color depending on change in a viewing angle.
Referring to FIG. 3, alignment states of two subpixels, that is, a first subpixel 320 and a second subpixel 340 are symmetrical with each other. The alignment states of the first and second subpixels 320 and 340 are simultaneously visible according to a direction viewed by a viewer, and the light intensity visible to the viewer is the sum of the light intensities of the respective subpixels. Specifically, each liquid crystal of the first and second subpixels 320 and 340 is visible to be horizontal alignment 312 and vertical alignment 314, respectively, as viewed from a right direction 310 with respect to the normal direction 330 of the LCD screen. Similarly, each liquid crystal of the first and second subpixels 320 and 340 is visible to be vertical alignment 352 and horizontal alignment 354, respectively, as viewed from a left direction 350 with respect to the normal direction 330 of the screen. Thus, the brightness of the screen in the respective directions 310 and 350 to the viewer may be identical and symmetrical with each other with respect to a vertical direction of the screen. So, the brightness of the screen in all directions, 310 330, and 350 to the viewer may be similar with each other. As a result, a degree of the change in the contrast ratio and color may be improved depending on the viewing angle.
FIG. 4 is a schematic diagram illustrating another example of a conventional invention for improving change in a contrast ratio and color depending on change in a viewing angle.
Referring to FIG. 4, an optical compensation film 420 is further included. The optical compensation film 420 has birefringent characteristics identical to that of liquid crystal molecules within an LCD panel 440. The alignment state of the liquid crystal molecules within the LCD panel 440 and an alignment state of virtual liquid crystal molecules of the optical compensation film 420 may be simultaneously visible to a viewer. The alignment state of the liquid crystal molecules within the LCD panel 440 and an alignment state of virtual liquid crystal molecules of the optical compensation film 420 are symmetrical with each other. The light intensity visible to the viewer may be the light intensities transmitted from the optical compensation film 420 and liquid crystal molecules in the LCD panel 440. Specifically, as viewed from the right direction 410, liquid crystal molecules within the LCD panel 440 are visible to be horizontal alignment 414, virtual liquid crystal molecules of the optical compensation film 420 are visible to be vertical alignment 412, and the light intensity visible to the viewer may be that transmitted from the virtual liquid crystal molecules in the vertical alignment 412 and liquid crystal molecules in the horizontal alignment 414. Similarly, as viewed from the left direction 450, the liquid crystal molecules within the LCD panel 440 are visible to be vertical alignment 454, the virtual liquid crystal molecules of the optical compensation film 420 are visible to be horizontal alignment 452, and the light intensity visible to the viewer may be that transmitted from the virtual liquid crystal molecules in the horizontal alignment 452 and the liquid crystal molecules in the vertical alignment 454. As viewed from the normal direction 430 of the LCD screen, the alignment state 434 of the liquid crystal molecules within the LCD panel 440 and the alignment state 432 of the virtual liquid crystal molecules within the optical compensation film 420 are visible to be symmetrical with each other. Thus, the brightness of the screen in the respective directions 410 and 450 to the viewer may be identical and symmetrical with each other with respect to a vertical direction of the screen. So, the brightness of the screen in all directions, 410 430, and 450 to the viewer may be similar with each other. As a result, changes in the contrast ratio and color depending on the change in the viewing angle may be improved, however, there still remain problems of brightness and the color change.
FIG. 5 is a graph illustrating results obtained by measuring changes in an emission spectrum depending on increases in viewing angles of an LCD according to a conventional invention. As illustrated in FIG. 5, the strength of the spectrum is gradually reduced along with an increase in the viewing angle. FIG. 6 is the normalized spectra, divided by the maximum value of each spectrum, depending on increases in viewing angles in order to accurately check the reduction degree of the strength of the spectrum for each wavelength range. As illustrated in FIG. 6, it can be seen that the strength of the spectrum normalized in a blue light region of about 400 to 500 nm is reduced along with the increase in the viewing angle, even though the strength of the spectrum normalized in another wavelength ranges is the same. This result shows that the strength of the spectrum normalized in the blue light region of about 400 to 500 nm is much more reduced along with the increase in the viewing angle in comparison with the other wavelength ranges. Thus, the change in the color along with the increase in the viewing angle such as being changed from white color to yellowish white color, that is, complementary color of blue color may incur deterioration of video quality. Also, a contrast ratio in a bright room may be reduced due to reflection of an external light, thereby incurring deterioration in visibility of the display.